Earlier quoted context omitted.
Does anyone on earth not have an obligation to be ethical? (Yes, I know there is no universally accepted definition of "ethical".)
Yes, I don't. Because when you say "act ethical" you mean "do what pleases me". This is why you can't put forth a definition, because if you did, it would expose your hypocrisy. And I'm not one bit interested in doing what pleases you. I'm only interested in doing what pleases ME (as is every other person on Earth, although most will never admit it out of cowardice). So no, I don't have ANY obligation at all towards…
"Pleasing" deals with emotions, so we can drop the facade of hyper-rationality right there. Cooperation is beneficial for an itdividuums' survival, as you rightfully state. It is indeed of such importance that the standards of cooperation have been internalized long ago – for non-sociopaths, altruism is an end in itself and creates positive feelings.
And if you insist on your way of looking at it you actually stopped half-way: what "pleases you" is /also/ just a useful heuristic to maximize you reproductive success. The warm feeling you get from winning the lottery is no more or less real than the warm feeling (other) people get when they see someone happily getting married.
For this whole system the borders between the individual and the group are fluid. While certainly, all else being equal, the individual's need usually trumps the group's, it is anything but clear-cut in most real scenarios. You may be willing to sacrifice someones life to save your own, but that can change if the other person is you daughter, when you get to old age or when it's not a 1:1 sacrifice but merely an assumption of a non-zero risk of death.